title: A non-apoptotic role for caspase-9 in muscle differentiation.
abstract: Caspases, a family of cysteine proteases most often investigated for their roles in apoptosis, have also been demonstrated to have functions that are vital for the efficient execution of cell differentiation. One such role that has been described is the requirement of caspase-3 for the differentiation of skeletal myoblasts into myotubes but, as yet, the mechanism leading to caspase-3 activation in this case remains elusive. Here, we demonstrate that caspase-9, an initiator caspase in the mitochondrial death pathway, is responsible for the activation of caspase-3 in differentiating C2C12 cells. Reduction of caspase-9 levels, using an shRNA construct, prevented caspase-3 activation and inhibited myoblast fusion. Myosin-heavy-chain expression, which accompanies myoblastic differentiation, was not caspase-dependent. Overexpression of Bcl-xL, a protein that inhibits caspase-9 activation, had the same effect on muscle differentiation as knockdown of caspase-9. These data suggest that the mitochondrial pathway is required for differentiation; however, the release of cytochrome c or Smac (Diablo) could not be detected, raising the possibility of a novel mechanism of caspase-9 activation during muscle differentiation.
authors.affiliation: National Centre for Biomedical Engineering Science and Department of Pharmacology and Therapeutics, National University of Ireland, Galway, Ireland.
authors.forename: Thomas V A
authors.initials: TV
authors.lastname: Murray
authors.forename: Jill M
authors.initials: JM
authors.lastname: McMahon
authors.forename: Breege A
authors.initials: BA
authors.lastname: Howley
authors.forename: Alanna
authors.initials: A
authors.lastname: Stanley
authors.forename: Thomas
authors.initials: T
authors.lastname: Ritter
authors.forename: Andrea
authors.initials: A
authors.lastname: Mohr
authors.forename: Ralf
authors.initials: R
authors.lastname: Zwacka
authors.forename: Howard O
authors.initials: HO
authors.lastname: Fearnhead
mesh_terms: D000818:Animals; D053148:Caspase 3 / Q000235:genetics / Q000378:metabolism; D053453:Caspase 9 / Q000235:genetics / Q000378:metabolism*; D002454:Cell Differentiation; D002460:Cell Line; D004789:Enzyme Activation; D051379:Mice; D032448:Myoblasts, Skeletal / Q000166:cytology* / Q000201:enzymology*; D034622:RNA Interference
chemical_list: D053148:Caspase 3; D053453:Caspase 9